This invention relates generally, but not exclusively, to the field of elevated access flooring, of a type in which a plurality of generally rectangular floor panels are supported above a base floor at the corners thereof, upon vertically adjustable pedestal supports for the purpose of providing space for cables, utilities, and other items connected with the various types of equipment normally disposed on the access floor.
Access floor panels are generally provided with a top surface of a decorative and wearing material more completely described as a high pressure laminate (HPL). This high pressure laminate consists of multiple sheets of phenolic resin impregnated kraft paper and an outer melamine surfaced decorative face which, under high pressure, controlled temperature and humidity, have been consolidated into a component of relatively uniform thickness. This surfacing component is adhesively bonded to the HPL receiving surface of the access floor panel employed.
The outer melamine plastic surface of the high pressure laminate is impervious to moisture penetration and thus provides a moisture barrier to one surface of the resin impregnated paper element which, on its opposite surface, exhibits a relatively high absorbent capability. Inherent in its manufacturing, the grain of all the paper sheets is uni-directional. Consequently, expansion or contraction of the resin element paper due to moisture absorption or loss is not uniform in all directions, but results in lateral dimensional changes in the ratio of approximately two to one.
Because of the melamine moisture barrier surface, a change in relative humidity affects the fibers of the resin kraft paper sheets opposite the melamine moisture barrier surface initially at the edges and the extreme fibers of the bonded surface. Given the propensity of the HPL for expansion or contraction in an approximate ratio of two to one, a change in relative humidity thus alters the stresses which existed within this component prior to the change in environment and creates an immediate tendency for the high pressure laminate to proceed into a positive or negative curvature. This inadequately restrained movement many times causes the delamination of high pressure laminate from the HPL receiving surface of the access floor panel.
The above-discussed effect has resulted in a relatively high rate of failure of access floor panels to remain stable and thus planar and usable. These panels must be replaced at substantial cost either to the manufacturer under warranty or to the buyer. Thus, it would be highly desirable to provide an inexpensive but efficient way to avoid such failures.